Handwheel obstruction detection and inertia compensation

ABSTRACT

A vehicle steering system includes a first sensor sensing a pinion angle of a handwheel and a second sensor sensing a torsion bar windup angle. An autonomous steering module generates a steering command having an input torque signal. A steering angle controller is configured to determine a filtered handwheel acceleration based on the pinion angle and the windup angle. The steering angle controller also determines an offset torque based on the filtered handwheel acceleration. Further, the steering angle controller applies the offset torque to the input torque signal to define a refined torque signal that compensates for inertia and off-center mass of the handwheel.

FIELD OF THE INVENTION

The disclosure made herein relates generally to driver assist and activesafety technologies in vehicles, and more particularly to steering anglecontrol that generates a torque signal that compensates for inertia andoff-center mass of the handwheel.

BACKGROUND OF THE INVENTION

Reversing a vehicle while towing a trailer can be challenging for manydrivers, particularly for drivers that drive with a trailer on aninfrequent basis or with various types of trailers. Backing a vehiclewith an attached trailer can be difficult as steering inputs arerequired that are opposite to steering inputs when backing the vehiclewithout a trailer attached to the vehicle, such that small errors insteering the vehicle are amplified by the trailer. These errors cancause the trailer to quickly depart from a desired path and may causedifficulties controlling the vehicle in a manner that limits thepotential for a jackknife condition to occur. Like other autonomous andsemi-autonomous vehicle systems, a trailer backup assist system mayreduce difficulties experienced by the driver performing such amaneuver. These autonomous and semi-autonomous vehicle systems mayprovide commands to an electronic steering controller that automaticallyoperates steered wheels of the vehicle. The accurate operation of theelectronic steering controller is critical to make autonomous andsemi-autonomous vehicle systems perform in a robust manner, so as to betrusted and relied upon by an operator of the vehicle.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a vehicle steeringsystem includes a first sensor sensing a pinion angle of a handwheel anda second sensor sensing a torsion bar windup angle. An autonomoussteering module generates a steering command having an input torquesignal. A steering angle controller is configured to determine afiltered handwheel acceleration based on the pinion angle and the windupangle. The steering angle controller also determines an offset torquebased on the filtered handwheel acceleration. Further, the steeringangle controller applies the offset torque to the input torque signal todefine a refined torque signal that compensates for inertia andoff-center mass of the handwheel.

According to another aspect of the present invention, a vehicle steeringsystem includes a sensor that senses a handwheel angle. An autonomoussteering module generates an input torque signal. A steering anglecontroller determines a filtered handwheel acceleration based on thehandwheel angle, determines an offset torque based on the filteredhandwheel acceleration, and generates a compensated torque signal basedon the offset torque and the input torque signal.

According to yet another aspect of the present invention, a methodincludes a step of sensing an angle of a handwheel. The method alsoincludes a step of generating a steering command having an input torquesignal. In addition, the method includes steps of determining a filteredhandwheel acceleration based on the angle and determining an offsettorque based on the filtered handwheel acceleration. Further, the methodincludes a step of generating a filtered compensated torque signal basedon the offset torque and the input torque signal to compensate forinertia and off-center mass of the handwheel.

These and other aspects, objects, and features of the present inventionwill be understood and appreciated by those skilled in the art uponstudying the following specification, claims, and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a top perspective view of a vehicle attached to a trailer withone embodiment of a trailer backup assist system;

FIG. 2 is a block diagram illustrating one embodiment of the trailerbackup assist system having a steering input device and a controller incommunication with a steering system;

FIG. 3 is a schematic diagram that illustrates the geometry of a vehicleand a trailer overlaid with a two-dimensional x-y coordinate system,identifying variables used to determine a kinematic relationship of thevehicle and the trailer for the trailer backup assist system, accordingto one embodiment;

FIG. 4 is a schematic block diagram illustrating portions of a curvatureroutine of the controller, according to an additional embodiment, andother components of the trailer backup assist system, according to suchan embodiment;

FIG. 5 is schematic block diagram of the curvature routine of FIG. 4,showing the feedback architecture and signal flow of the controller,according to such an embodiment;

FIG. 6 is a schematic diagram showing a relationship between a hitchangle and a steering angle of the vehicle as it relates to curvature ofthe trailer and a jackknife angle;

FIG. 7 is a plan view of one embodiment of a steering input devicehaving a rotatable knob for operating the trailer backup assist system;

FIG. 8 is a plan view of another embodiment of a rotatable knob forselecting a desired curvature of a trailer and a corresponding schematicdiagram illustrating a vehicle and a trailer with various trailercurvature paths correlating with desired curvatures that may beselected;

FIG. 9 is a schematic diagram showing a backup sequence of a vehicle anda trailer implementing various curvature selections with the trailerbackup assist system, according to one embodiment;

FIG. 10 is a flow diagram illustrating a method of operating a trailerbackup assist system using an operating routine for steering a vehiclereversing a trailer with the desired curvature, according to oneembodiment;

FIG. 11 is a flow diagram illustrating a method of operating a trailerbackup assist system using a steering angle limitation routine,according to one embodiment;

FIG. 12 is a graphical representation of the steering wheel anglerelative to the hitch angle for one embodiment of a vehicle and atrailer, illustrating physical angle limits and various adaptive anglelimits;

FIG. 13 is a block diagram illustrating one embodiment of the steeringsystem having a controller in communication with the trailer backupassist system and a park assist system;

FIG. 14 is a flow chart of conditional transitions of an angle-basedsteering control routine, showing the order of the lowest numberedtransition to the highest;

FIG. 15 is a graphical representation of transitions of angle control bythe angle-based steering control routine;

FIG. 16 is flow diagram illustrating a method of operating a steeringsystem using the angle-based steering control routine, according to oneembodiment;

FIG. 17 is schematic diagram of a handwheel operably coupled withsteerable wheels of a vehicle, showing angle sensors and a torquesensor;

FIG. 18 is a block diagram illustrating signal flow of one embodiment ofthe steering system;

FIG. 19 is a flow diagram illustrating a method of operating a steeringsystem using a torque signal compensation routine, according to oneembodiment; and

FIGS. 20A-B are graphical representations of an exemplary torque signalcompensated with a torque signal compensation routine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For purposes of description herein, it is to be understood that thedisclosed trailer backup assist system and the related methods mayassume various alternative embodiments and orientations, except whereexpressly specified to the contrary. It is also to be understood thatthe specific devices and processes illustrated in the attached drawings,and described in the following specification are simply exemplaryembodiments of the inventive concepts defined in the appended claims.While various aspects of the trailer backup assist system and therelated methods are described with reference to a particularillustrative embodiment, the disclosed invention is not limited to suchembodiments, and additional modifications, applications, and embodimentsmay be implemented without departing from the disclosed invention.Hence, specific dimensions and other physical characteristics relatingto the embodiments disclosed herein are not to be considered aslimiting, unless the claims expressly state otherwise.

Referring to FIGS. 1-13, reference numeral 10 generally designates atrailer backup assist system for controlling a backing path of a trailer12 attached to a vehicle 14 by allowing a driver of the vehicle 14 tospecify a desired curvature 26 of the backing path of the trailer 12. Inone embodiment, the trailer backup assist system 10 automatically steersthe vehicle 14 to guide the trailer 12 on the desired curvature 26 ofthe backing path as a driver uses the accelerator and brake pedals tocontrol the reversing speed of the vehicle 14. To monitor the positionof the trailer 12 relative to the vehicle 14, the trailer backup assistsystem 10 may include a sensor or sensor system 16 that senses orotherwise determines a hitch angle γ between the trailer 12 and thevehicle 14. In one embodiment, the sensor system 16 may include a hitchangle sensor 44, such as a vision-based sensor that employs a camera 46on the vehicle 14 to monitor a target 52 on the trailer 12 to measurethe hitch angle γ. The vehicle 14 is autonomously steered with asteering system 62 that controls a steering angle δ of the front wheelsof the vehicle 14 within physical angle limits 20 of the steering system62 and any adaptive angle limits 23, which may be generated based on areversing speed of the vehicle 14, the hitch angle γ, and a maximumhitch angle rate. Restricting the steering command to the adaptive anglelimit 23 may prevent the steering system 62 from exceeding the maximumhitch angle rate, and thereby avoid undesired hitch angle conditionsoutside the desired curvature 26, such as a jackknife condition.

Referring generally to FIGS. 13-20B, the steering system 62 is furtherillustrated and defined to operate multiple autonomous steering modules,including the trailer backup assist system 10 and other autonomoussteering modules, such as an active park assist system 202. To arbitrateand control the steering system 62, an angle-based steering controlroutine 206 of the steering angle controller 200 is configured toreceive the steering angle commands from multiple steering modules, andwhen multiple steering angle commands are present, generate a refinedsteering angle command for the steering angle controller 200 to operatethe steered wheels 64 of the vehicle. The steering angle controller 200receives the multiple steering angle commands and generates the refinedsteering angle command for steering the vehicle based on acceptablesteering column torque conditions for the respective steering module. Assuch, the refined steering angle command may be substantially equal toone of the steering angle commands when the other potential steeringangle commands have transitioned to an inactive arbitration state. Toaccurately control the steering angle with the refined steering anglecommand, the steering angle controller 200 may also process a torquesignal compensation routine that determines a filtered handwheelacceleration based on the handwheel angle, determines an offset torquebased on the filtered handwheel acceleration and mass properties, andultimately generates a compensated torque signal based on the offsettorque and the input torque signal. The compensated torque signalcompensates for inertia and off-center mass of the handwheel, whereby ahigh torque value associated with a sudden change in direction of thepinion angle is reduced in the refined torque signal to prevent therefined torque signal from errantly exceeding a torque threshold, whichis indicative of an object obstructing rotation of the handwheel andcauses the respective autonomous steering module to be placed in aninactive arbitration state, such as a fault condition.

With reference to the embodiment shown in FIG. 1, the vehicle 14 is apickup truck embodiment that is equipped with one embodiment of thetrailer backup assist system 10 for controlling the backing path of thetrailer 12 that is attached to the vehicle 14. Specifically, the vehicle14 is pivotally attached to one embodiment of the trailer 12 that has abox frame 32 with an enclosed cargo area 34, a single axle having aright wheel assembly and a left wheel assembly, and a tongue 36longitudinally extending forward from the enclosed cargo area 34. Theillustrated trailer 12 also has a trailer hitch connector in the form ofa coupler assembly 38 that is connected to a vehicle hitch connector inthe form of a hitch ball 40. The coupler assembly 38 latches onto thehitch ball 40 to provide a pivoting ball joint connection 42 that allowsfor articulation of the hitch angle γ. It should be appreciated thatadditional embodiments of the trailer 12 may alternatively couple withthe vehicle 14 to provide a pivoting connection, such as by connectingwith a fifth wheel connector. It is also contemplated that additionalembodiments of the trailer may include more than one axle and may havevarious shapes and sizes configured for different loads and items, suchas a boat trailer or a flatbed trailer.

Still referring to FIG. 1, the sensor system 16 in the illustratedembodiment includes a vision-based hitch angle sensor 44 for estimatingthe hitch angle γ between the vehicle 14 and the trailer 12. Theillustrated hitch angle sensor 44 employs a camera 46 (e.g. videoimaging camera) that may be located proximate an upper region of thevehicle tailgate 48 at the rear of the vehicle 14, as shown, such thatthe camera 46 may be elevated relative to the tongue 36 of the trailer12. The illustrated camera 46 has an imaging field of view 50 locatedand oriented to capture one or more images of the trailer 12, includinga region containing one or more desired target placement zones for atleast one target 52 to be secured. Although it is contemplated that thecamera 46 may capture images of the trailer 12 without a target 52 todetermine the hitch angle γ, in the illustrated embodiment, the trailerbackup assist system 10 includes a target 52 placed on the trailer 12 toallow the trailer backup assist system 10 to utilize informationacquired via image acquisition and processing of the target 52. Forinstance, the illustrated camera 46 may include a video imaging camerathat repeatedly captures successive images of the trailer 12 that may beprocessed to identify the target 52 and its location on the trailer 12for determining movement of the target 52 and the trailer 12 relative tothe vehicle 14 and the corresponding hitch angle γ. It should also beappreciated that the camera 46 may include one or more video imagingcameras and may be located at other locations on the vehicle 14 toacquire images of the trailer 12 and the desired target placement zone,such as on a passenger cab 54 of the vehicle 14 to capture images of agooseneck trailer. Furthermore, it is contemplated that additionalembodiments of the hitch angle sensor 44 and the sensor system 16 forproviding the hitch angle γ may include one or a combination of apotentiometer, a magnetic-based sensor, an optical sensor, a trailer yawrate sensor, a proximity sensor, an ultrasonic sensor, a rotationalsensor, a capacitive sensor, an inductive sensor, or a mechanical basedsensor, such as a mechanical sensor assembly mounted to the pivotingball joint connection 42, energy transducers of a reverse aid system, ablind spot system, and/or a cross traffic alert system, and otherconceivable sensors or indicators of the hitch angle γ to supplement orbe used in place of the vision-based hitch angle sensor 44.

With reference to the embodiment of the trailer backup assist system 10shown in FIG. 2, the hitch angle sensor 44 is illustrated generally as ameans to estimate the hitch angle γ and communicate with the trailerbackup assist system 10. The illustrated embodiment of the trailerbackup assist system 10 also receives vehicle and trailer status-relatedinformation from additional sensors and devices. This informationincludes positioning information from a positioning device 56, which mayinclude a global positioning system (GPS) on the vehicle 14 or a handleddevice, to determine a coordinate location of the vehicle 14 and thetrailer 12 based on the location of the positioning device 56 withrespect to the trailer 12 and/or the vehicle 14 and based on theestimated hitch angle γ. The positioning device 56 may additionally oralternatively include a dead reckoning system for determining thecoordinate location of the vehicle 14 and the trailer 12 within alocalized coordinate system based at least on vehicle speed, steeringangle, and hitch angle γ. Other vehicle information received by thetrailer backup assist system 10 may include a speed of the vehicle 14from a speed sensor 58 and a yaw rate of the vehicle 14 from a yaw ratesensor 60. It is contemplated that in additional embodiments, the hitchangle sensor 44 and other vehicle sensors and devices may provide sensorsignals or other information, such as proximity sensor signals orsuccessive images of the trailer 12, that the controller of the trailerbackup assist system 10 may process with various routines to supplementthe hitch angle sensor 44 in estimating hitch angle γ or an indicatorthereof, such as a range of hitch angles.

As also shown in FIG. 2, one embodiment of the trailer backup assistsystem 10 is in communication with a power assist steering system 62 ofthe vehicle 14 to operate the steered wheels 64 (FIG. 1) of the vehicle14 for moving the vehicle 14 in such a manner that the trailer 12generally reacts in accordance with the desired curvature 26 of thetrailer 12. In the illustrated embodiment, the steering system 62 is anelectric power-assisted steering (EPAS) system that includes an electricsteering motor 66 for turning the steered wheels 64 (FIG. 1) to asteering angle based on a steering command, whereby the steering anglemay be sensed by a steering angle sensor 67 of the steering system 62.Due to the size of wheel wells and tire dimensions, among othercomponents of the vehicle 14, the steering system 62 may be physicallyconstrained in the amount the steered wheels 64 may be freely turned bythe electric steering motor 66, which thereby defines the physicalsteering angle limits 20 of the steering system 62. For instance, thephysical steering angle limits 20 may be determined by the minimumturning radius achievable by the vehicle 14. Accordingly, the physicalsteering angle limits 20 may vary between types and configurations ofdifferent vehicles. In addition, the steering system 62 may also benaturally constrained by the maximum controllable steering angle rate ofthe steering system 62, which may be determined by the capacity of theelectric steering motor 66, among other associated components of thesteering system 62. The controllable rate of adjusting the steeringangle δ with the steering system 62 may be used by the trailer backupassist system 10 to regulate the steering commands for preventing theresulting hitch angle conditions from deviating outside the desiredcurvature 26 of the trailer 12.

With further reference to FIG. 2, the steering command may be providedby the trailer backup assist system 10 for autonomously steering duringa backup maneuver and may alternatively be provided by other vehiclesteering assistance systems or modules. It is also contemplated that asteering command may be provided manually via a rotational position(e.g., steering wheel angle) of a steering wheel or handwheel 68(FIG. 1) for manual operation of the vehicle. In the illustratedembodiment, the handwheel 68 of the vehicle 14 is mechanically coupledwith the steered wheels 64 of the vehicle 14, such that the handwheel 68moves in concert with steered wheels 64, preventing manual interventionwith the handwheel 68 during autonomous steering. More specifically, atorque sensor 70 is provided on the power assist steering system 62 thatsenses torque on the handwheel 68 that is not expected from autonomouscontrol of the handwheel 68 and therefore indicative of manualintervention, whereby the trailer backup assist system 10 may alert thedriver to discontinue manual intervention with the handwheel 68 and/ordiscontinue autonomous steering.

In additional embodiments, some vehicles have a power assist steeringsystem 62 that allows a handwheel 68 to be partially decoupled frommovement of the steered wheels 64 of such a vehicle. Accordingly, thehandwheel 68 can be rotated independent of the manner in which the powerassist steering system 62 of the vehicle controls the steered wheels 64(e.g., autonomous steering as commanded by the trailer backup assistsystem 10). As such, in these types of vehicles where the handwheel 68can be selectively decoupled from the steered wheels 64 to allowindependent operation thereof, the handwheel 68 may be used as asteering input device 18 for the trailer backup assist system 10, asdisclosed in greater detail herein.

Referring again to the embodiment illustrated in FIG. 2, the powerassist steering system 62 may provide the controller 28 of the trailerbackup assist system 10 with information relating to a rotationalposition of steered wheels 64 of the vehicle 14, such as the steeringangle δ of the steered wheels 64. The controller 28 in the illustratedembodiment processes the current steering angle δ, in addition to othervehicle 14 and trailer 12 conditions to guide the trailer 12 along thedesired curvature 26. It is conceivable that the trailer backup assistsystem 10, in additional embodiments, may be an integrated component ofthe power assist steering system 62. For example, in such an alternativeembodiment the power assist steering system 62 may include an algorithmfor generating vehicle steering information and commands as a functionof all or a portion of information received from the steering inputdevice 18, the hitch angle sensor 44, the power assist steering system62, a vehicle brake control system 72, a powertrain control system 74,and the other vehicle sensors and devices.

As also illustrated in FIG. 2, the vehicle brake control system 72, alsoreferred to as the braking system, may also communicate with thecontroller 28 to provide the trailer backup assist system 10 withbraking information, such as vehicle wheel speed, and to receive brakingcommands from the controller 28. For instance, vehicle speed informationcan be determined from individual wheel speeds as monitored by the brakecontrol system 72. Vehicle speed may also be determined from thepowertrain control system 74, the speed sensor 58, and the positioningdevice 56, among other conceivable means. In some embodiments,individual wheel speeds can also be used to determine a vehicle yawrate, which can be provided to the trailer backup assist system 10 inthe alternative or in addition to the vehicle yaw rate sensor 60. Incertain embodiments, the trailer backup assist system 10 can providevehicle braking information to the brake control system 72 for allowingthe trailer backup assist system 10 to control braking of the vehicle 14during backing of the trailer 12. For instance, the trailer backupassist system 10 in some embodiments may regulate speed of the vehicle14 during backing of the trailer 12, which can reduce the potential forunacceptable trailer backup conditions. Examples of unacceptable trailerbackup conditions include, but are not limited to, a vehicle 14 overspeed condition, a high hitch angle rate, trailer angle dynamicinstability, a calculated theoretical trailer jackknife condition(defined by a maximum vehicle steering angle, drawbar length, towvehicle wheelbase, and an effective trailer length), or physical contactjackknife limitation (defined by an angular displacement limit relativeto the vehicle 14 and the trailer 12), and the like. It is alsodisclosed herein that the trailer backup assist system 10 can issue analert signal corresponding to a notification of an actual, impending,and/or anticipated unacceptable trailer backup condition. Further, inone embodiment, the braking system 72 may be controlled with the trailerbackup assist system 10 to autonomously limit speed of the vehicle 14during a backing maneuver for the maximum hitch angle rate generated bythe trailer backup assist system 10 to remain substantially constant,such that the vehicle 14 is limited to reversing at lower speeds as thehitch angle increases. The maximum hitch angle rate remainingsubstantially constant may also allow the adaptive steering angle limits23 to not further restrict adjustments to the steering angle as thehitch angle increases.

The powertrain control system 74, as shown in the embodiment illustratedin FIG. 2, may similarly interact with the trailer backup assist system10 for regulating speed and acceleration of the vehicle 14 duringbacking of the trailer 12. As mentioned above, regulation of the speedof the vehicle 14 may be used to limit the potential for unacceptabletrailer backup conditions such as, for example, jackknifing and trailerangle dynamic instability. Similar to high-speed considerations as theyrelate to unacceptable trailer backup conditions, high acceleration andhigh dynamic driver curvature requests can also lead to suchunacceptable trailer backup conditions.

With continued reference to FIG. 2, the trailer backup assist system 10in the illustrated embodiment may communicate with one or more devices,including a vehicle alert system 76, which may prompt visual, auditory,and tactile warnings. For instance, vehicle brake lights 78 and vehicleemergency flashers may provide a visual alert and a vehicle horn 79and/or speaker 81 may provide an audible alert. Additionally, thetrailer backup assist system 10 and/or vehicle alert system 76 maycommunicate with a human machine interface (HMI) 80 for the vehicle 14.The HMI 80 may include a vehicle display 82, such as a center-stackmounted navigation or entertainment display (FIG. 1). Further, thetrailer backup assist system 10 may communicate via wirelesscommunication with another embodiment of the HMI 80, such as with one ormore handheld or portable devices, including one or more smartphones.The portable device may also include the display 82 for displaying oneor more images and other information to a user. For instance, theportable device may display one or more images of the trailer 12 and anindication of the estimated hitch angle on the display 82. In addition,the portable device may provide feedback information, such as visual,audible, and tactile alerts.

As further illustrated in FIG. 2, the trailer backup assist system 10includes a steering input device 18 that is connected to the controller28 for allowing communication of information therebetween. It isdisclosed herein that the steering input device 18 can be coupled to thecontroller 28 in a wired or wireless manner. The steering input device18 provides the trailer backup assist system 10 with informationdefining the desired backing path of travel of the trailer 12 for thecontroller 28 to process and generate steering commands. Morespecifically, the steering input device 18 may provide a selection orpositional information that correlates with a desired curvature 26 ofthe desired backing path of travel of the trailer 12. Also, the commandsprovided by the steering input device 18 can include informationrelating to a commanded change in the path of travel, such as anincremental change in the desired curvature 26, and information relatingto an indication that the trailer 12 is to travel along a path definedby a longitudinal centerline axis of the trailer 12, such as a desiredcurvature value of zero that defines a substantially straight path oftravel for the trailer. As will be discussed below in more detail, thesteering input device 18, according to one embodiment, may include amovable control input device separate from the handwheel for allowing adriver of the vehicle 14 to command desired trailer steering actions orotherwise select and alter a desired curvature. For instance, themoveable control input device may be a rotatable knob 30, which can berotatable about a rotational axis extending through a top surface orface of the knob 30. In other embodiments, the rotatable knob 30 may berotatable about a rotational axis extending substantially parallel to atop surface or face of the rotatable knob 30. Furthermore, the steeringinput device 18, according to additional embodiments, may includealternative devices for providing a desired curvature 26 or otherinformation defining a desired backing path, such as a joystick, akeypad, a series of depressible buttons or switches, a sliding inputdevice, various user interfaces on a touch-screen display, a visionbased system for receiving gestures, a control interface on a portabledevice, and other conceivable input devices as generally understood byone having ordinary skill in the art. It is contemplated that thesteering input device 18 may also function as an input device for otherfeatures, such as providing inputs for other vehicle features orsystems.

Still referring to the embodiment shown in FIG. 2, the controller 28 isconfigured with a microprocessor 84 to process logic and routines storedin memory 86 that receive information from the sensor system 16,including the hitch angle sensor 44, the steering input device 18, thesteering system 62, the vehicle brake control system 72, the trailerbraking system, the powertrain control system 74, and other vehiclesensors and devices. The controller 28 may generate vehicle steeringinformation and commands as a function of all or a portion of theinformation received. Thereafter, the vehicle steering information andcommands may be provided to the steering system 62 for affectingsteering of the vehicle 14 to achieve a commanded path of travel for thetrailer 12. The controller 28 may include the microprocessor 84 and/orother analog and/or digital circuitry for processing one or moreroutines. Also, the controller 28 may include the memory 86 for storingone or more routines, including a steering angle limitation routine 130,an operating routine 132, and a curvature routine 98. It should beappreciated that the controller 28 may be a stand-alone dedicatedcontroller or may be a shared controller integrated with other controlfunctions, such as integrated with the sensor system 16, the steeringsystem 62, and other conceivable onboard or off-board vehicle controlsystems.

With reference to FIG. 3, we now turn to a discussion of vehicle andtrailer information and parameters used to calculate a kinematicrelationship between a curvature of a path of travel of the trailer 12and the steering angle of the vehicle 14 towing the trailer 12. Thekinematic relationship can be usefully for various routines of a trailerbackup assist system 10, including for use by a curvature routine 98 ofthe controller 28 in one embodiment. To determine such a kinematicrelationship, certain assumptions may be made with regard to parametersassociated with the vehicle/trailer system. Examples of such assumptionsinclude, but are not limited to, the trailer 12 being backed by thevehicle 14 at a relatively low speed, wheels of the vehicle 14 and thetrailer 12 having negligible (e.g., no) slip, tires of the vehicle 14having negligible (e.g., no) lateral compliance, tires of the vehicle 14and the trailer 12 having negligible (e.g., no) deformation, actuatordynamics of the vehicle 14 being negligible, and the vehicle 14 and thetrailer 12 exhibiting negligible (e.g., no) roll or pitch motions, amongother conceivable factors with the potential to have an effect oncontrolling the trailer 12 with the vehicle 14.

As shown in FIG. 3, for a system defined by a vehicle 14 and a trailer12, the kinematic relationship is based on various parameters associatedwith the vehicle 14 and the trailer 12. These parameters include:

δ: steering angle at steered front wheels of the vehicle;

α: yaw angle of the vehicle;

β: yaw angle of the trailer;

γ: hitch angle (γ=β−α);

W: wheel base of the vehicle;

L: length between hitch point and rear axle of the vehicle;

D: distance between hitch point and axle of the trailer or effectiveaxle for a multiple axle trailer (axle length may be an equivalent); and

r₂: curvature radius for the trailer.

One embodiment of a kinematic relationship based on trailer path radiusof curvature r₂ at the midpoint of an axle of the trailer 12, steeringangle δ of the steered wheels 64 of the vehicle 14, and the hitch angleγ can be expressed in the equation provided below. As such, if the hitchangle γ is provided, the trailer path curvature κ₂ can be controlledbased on regulating the steering angle δ (where) {dot over (β)} istrailer yaw rate and {dot over (η)} is trailer velocity).

$\kappa_{2} = {\frac{1}{r_{2}} = {\frac{\overset{.}{\beta}}{\overset{.}{\eta}} = \frac{{\left( {W + \frac{{KV}^{2}}{g}} \right)\sin\;\gamma} + {L\;\cos\;{\gamma tan}\;\delta}}{D\left( {{\left( {W + \frac{{KV}^{2}}{g}} \right)\cos\;\gamma} - {L\;\sin\;{\gamma tan}\;\delta}} \right)}}}$

This relationship can be expressed to provide the steering angle δ as afunction of trailer path curvature κ₂ and hitch angle γ.

$\delta = {{\tan^{- 1}\left( \frac{\left( {W + \frac{{KV}^{2}}{g}} \right)\left\lbrack {{\kappa_{2}D\;\cos\;\gamma} - {\sin\;\gamma}} \right\rbrack}{{{DL}\;\kappa_{2}\;\sin\;\gamma} + {L\;\cos\;\gamma}} \right)} = {F\left( {\gamma,\kappa_{2},K} \right)}}$

Through the use of the equation for providing steering angle, acorresponding steering command can be generated by the curvature routine98 for controlling the power assist steering system 62 of the vehicle14. Accordingly, for a particular vehicle and trailer combination,certain parameters (e.g., D, W, and L) of the kinematic relationship areconstant and assumed known, while other parameters (e.g. speed of thevehicle and hitch angle) are sensed or otherwise determined by thesystem. V is the vehicle longitudinal speed and g is the accelerationdue to gravity. K is a speed dependent parameter which when set to zeromakes the calculation of steering angle independent of vehicle speed.Trailer path curvature κ₂ can be determined from the driver input viathe steering input device 18. However, constant, vehicle-specificparameters of the kinematic relationship can be predefined in anelectronic control system of the vehicle 14 and constant,trailer-specific parameters of the kinematic relationship can beinputted by a driver of the vehicle 14, determined from sensed trailerbehavior in response to vehicle steering commands, or otherwisedetermined from signals provided by the trailer 12. For instance, theknown trailer parameters can be provided by the user obtaining theparameters, such as by taking measurements with a tape measure, andmanually entering the parameters into memory of the system (e.g. via theHMI 80 of the vehicle). In an additional embodiment, the knownparameters of the trailer 12 (e.g. trailer length D, wheel base of thetrailer, and trailer height) and any other trailer data (e.g. thepresence of trailer brakes, and the trailer load capabilities) may beautomatically obtained by the user and may be automatically transmittedto the trailer backup assist system 10 by a user scanning a uniqueidentifier on the attached trailer 12. Such a unique identifier mayinclude a radio frequency identifier (RFID) chip, a quick response (QR)code, or similar arrangement on the trailer that can be interpreted anddecoded to recover the data, often by a smartphone device with wirelessinternet connectivity. Moreover, an electronic camera on a smartphonecould view and decode a QR code sticker permanently attached to thetrailer 12 to determine the unique trailer identifier, such as a serialnumber, and then wirelessly contact a related trailer database on theinternet or a private server to download the trailer parametersassociated with the unique trailer identifier to the phone and/or thetrailer backup assist system. In the event that the trailer database isnot able to provide the necessary parameters of the trailer, the usercould also apply a QR code sticker containing a unique identifier to thetrailer and manually input the trailer parameters to associate the QRcode with the trailer in the future. It is also contemplated that otherembodiments may use alternative trailer detection techniques toautomatically determine the trailer parameters.

In an additional embodiment, an assumption may be made by the curvatureroutine 98 that a longitudinal distance L between the pivotingconnection and the rear axle of the vehicle 14 is equal to zero forpurposes of operating the trailer backup assist system 10 when agooseneck trailer or other similar trailer is connected with the a hitchball or a fifth wheel connector located over a rear axle of the vehicle14. The assumption is that the pivoting connection with the trailer 12is substantially vertically aligned with the rear axle of the vehicle14. When such an assumption is made, the controller 28 may generate thesteering angle command for the vehicle 14 as a function independent ofthe longitudinal distance L between the pivoting connection and the rearaxle of the vehicle 14. It is appreciated that the gooseneck trailermentioned herein generally refers to the tongue configuration beingelevated to attach with the vehicle 14 at an elevated location over therear axle, such as within a bed of a truck, whereby embodiments of thegooseneck trailer may include flatbed cargo areas, enclosed cargo areas,campers, cattle trailers, horse trailers, lowboy trailers, and otherconceivable trailers with such a tongue configuration.

Yet another embodiment of the curvature routine 98 of the trailer backupassist system 10 is illustrated in FIG. 4, which depicts the generalarchitectural layout whereby a measurement module 88, a hitch angleregulator 90, and a curvature regulator 92 are routines that may bestored in the memory 86 of the controller 28. In the illustrated layout,the steering input device 18 provides a desired curvature κ₂ value tothe curvature regulator 92 of the controller 28, which may be determinedfrom the desired backing path 26 that is input with the steering inputdevice 18. The curvature regulator 92 computes a desired hitch angleγ(d) based on the current desired curvature κ₂ along with the steeringangle δ provided by a measurement module 88 in this embodiment of thecontroller 28. The measurement module 88 may be a memory device separatefrom or integrated with the controller 28 that stores data from sensorsof the trailer backup assist system 10, such as the hitch angle sensor44, the vehicle speed sensor 58, the steering angle sensor, oralternatively the measurement module 88 may otherwise directly transmitdata from the sensors without functioning as a memory device. Once thedesired hitch angle γ(d) is computed by the curvature regulator 92 thehitch angle regulator 90 generates a steering angle command based on thecomputed desired hitch angle γ(d) as well as a measured or otherwiseestimated hitch angle γ(m) and a current velocity of the vehicle 14. Thesteering angle command is supplied to the power assist steering system62 of the vehicle 14, which is then fed back to the measurement module88 to reassess the impacts of other vehicle characteristics impactedfrom the implementation of the steering angle command or other changesto the system. Accordingly, the curvature regulator 92 and the hitchangle regulator 90 continually process information from the measurementmodule 88 to provide accurate steering angle commands that place thetrailer 12 on the desired curvature κ₂ and the desired backing path 26,without substantial overshoot or continuous oscillation of the path oftravel about the desired curvature κ₂.

As also shown in FIG. 5, the embodiment of the curvature routine 98shown in FIG. 4 is illustrated in a control system block diagram.Specifically, entering the control system is an input, κ₂, whichrepresents the desired curvature 26 of the trailer 12 that is providedto the curvature regulator 92. The curvature regulator 92 can beexpressed as a static map, p(κ₂, δ), which in one embodiment is thefollowing equation:

${p\left( {\kappa_{2},\delta} \right)} = {\tan^{- 1}\left( \frac{{\kappa_{2}{DW}} + {L\;{\tan(\delta)}}}{{\kappa_{2}{DL}\;{\tan(\delta)}} - W} \right)}$

Where,

κ₂ represents the desired curvature of the trailer 12 or 1/r₂ as shownin FIG. 3;

δ represents the steering angle;

L represents the distance from the rear axle of the vehicle 14 to thehitch pivot point;

D represents the distance from the hitch pivot point to the axle of thetrailer 12; and

W represents the distance from the rear axle to the front axle of thevehicle 14.

With further reference to FIG. 5, the output hitch angle of p(κ₂, δ) isprovided as the reference signal, γ_(ref), for the remainder of thecontrol system, although the steering angle δ value used by thecurvature regulator 92 is feedback from the non-linear function of thehitch angle regulator 90. It is shown that the hitch angle regulator 90uses feedback linearization for defining a feedback control law, asfollows:

${g\left( {u,\gamma,v} \right)} = {\delta = {\tan^{- 1}\left( {\frac{W}{v\left( {1 + {\frac{L}{D}{\cos(\gamma)}}} \right)}\left( {{\frac{v}{D}{\sin(\gamma)}} - u} \right)} \right)}}$

As also shown in FIG. 5, the feedback control law, g(u, γ, ν), isimplemented with a proportional integral (PI) controller, whereby theintegral portion substantially eliminates steady-state tracking error.More specifically, the control system illustrated in FIG. 58 may beexpressed as the following differential-algebraic equations:

$\mspace{20mu}{{\overset{.}{\gamma}(t)} = {{\frac{v(t)}{D}{\sin\left( {\gamma(t)} \right)}} + {\left( {1 + {\frac{L}{D}{\cos\left( {\gamma(t)} \right)}}} \right)\frac{v(t)}{W}\overset{\_}{\delta}}}}$${\tan(\delta)} = {\overset{\_}{\delta} = {\frac{W}{{v(t)}\left( {1 + {\frac{L}{D}{\cos\left( {\gamma(t)} \right)}}} \right)}\left( {{K_{P}\left( {{p\left( {\kappa_{2},\delta} \right)} - {\gamma(t)}} \right)} - {\frac{v(t)}{D}{\sin\left( {\gamma(t)} \right)}}} \right)}}$

It is contemplated that the PI controller may have gain terms based ontrailer length D since shorter trailers will generally have fasterdynamics. In addition, the hitch angle regulator 90 may be configured toprevent the desired hitch angle γ(d) to reach or exceed a jackknifeangle γ(j), as computed by the controller or otherwise determined by thetrailer backup assist system 10, as disclosed in greater detail herein.

Referring now to FIG. 6, in the illustrated embodiments of the disclosedsubject matter, it may be desirable to limit the potential for thevehicle 14 and the trailer 12 to attain a jackknife angle (i.e., thevehicle/trailer system achieving a jackknife condition). A jackknifeangle γ(j) refers to a hitch angle γ that while backing cannot beovercome by the maximum steering input for a vehicle such as, forexample, the steered front wheels of the vehicle 14 being moved amaximum rate of steering angle change to a maximum steered angle δ orphysical steering angle limit 20. The jackknife angle γ(j) is a functionof a maximum wheel angle (i.e. a physical steering angle limit 20) forthe steered wheels of the vehicle 14, the wheel base W of the vehicle14, the distance L between hitch point and the rear axle of the vehicle14, and the length D between the hitch point and the axle of the trailer12 or the effective axle when the trailer 12 has multiple axles. Whenthe hitch angle γ for the vehicle 14 and the trailer 12 achieves orexceeds the jackknife angle γ(j), the vehicle 14 may be pulled forwardto reduce the hitch angle γ.

A kinematic model representation of the vehicle 14 and the trailer 12can also be used to determine a jackknife angle for the vehicle-trailercombination. Accordingly, with reference to FIGS. 3 and 6, the physicalsteering angle limit 20 for the steered front wheels 64 requires thatthe hitch angle γ cannot exceed the jackknife angle γ(j), which is alsoreferred to as a critical hitch angle γ. Thus, under the limitation thatthe hitch angle γ cannot exceed the jackknife angle γ(j), the jackknifeangle γ(j) is the hitch angle γ that maintains a circular motion for thevehicle/trailer system when the steered wheels 64 are at a maximumsteering angle γ(max) or the physical steering angle limit 20. Thesteering angle for circular motion with hitch angle γ is defined by thefollowing equation.

${\tan\;\delta_{\max}} = \frac{w\;\sin\;\gamma_{\max}}{D + {L\;\cos\;\gamma_{\max}}}$

Solving the above equation for hitch angle γ allows jackknife angle γ(j)to be determined. This solution, which is shown in the followingequation, can be used in implementing trailer backup assistfunctionality in accordance with the disclosed subject matter formonitoring hitch angle γ in relation to jackknife angle.

${\cos\;\overset{\_}{\gamma}} = \frac{{- b} \pm \sqrt{b^{2} - {4\;{ac}}}}{2\; a}$

where,

a=L² tan² δ(max)+W²;

b=2 LD tan² δ(max); and

c=D² tan² δ(max)−W².

In certain instances of backing the trailer 12, a jackknife enablingcondition can arise based on current operating parameters of the vehicle14 in combination with a corresponding hitch angle γ. This condition canbe indicated when one or more specified vehicle operating thresholds aremet while a particular hitch angle γ is present. For example, althoughthe particular hitch angle γ is not currently at the jackknife angle forthe vehicle 14 and attached trailer 12, certain vehicle operatingparameters can lead to a rapid (e.g., uncontrolled) transition of thehitch angle γ to the jackknife angle for a current commanded trailercurvature and/or can reduce an ability to steer the trailer 12 away fromthe jackknife angle.

Jackknife determining information may be received by the controller 28,according to one embodiment, to process and characterize a jackknifeenabling condition of the vehicle-trailer combination at a particularpoint in time (e.g., at the point in time when the jackknife determininginformation was sampled). Examples of the jackknife determininginformation include, but are not limited to, information characterizingan estimated hitch angle γ, information characterizing a vehicleaccelerator pedal transient state, information characterizing a speed ofthe vehicle 14, information characterizing longitudinal acceleration ofthe vehicle 14, information characterizing a brake torque being appliedby a brake system of the vehicle 14, information characterizing apowertrain torque being applied to driven wheels of the vehicle 14, andinformation characterizing the magnitude and rate of driver requestedtrailer curvature. In this regard, jackknife determining informationwould be continually monitored, such as by an electronic control unit(ECU), such as the controller 28, that carries out trailer backup assistfunctionality. After receiving the jackknife determining information, aroutine may process the jackknife determining information fordetermining if the vehicle-trailer combination attained the jackknifeenabling condition at the particular point in time. The objective of theoperation for assessing the jackknife determining information isdetermining if a jackknife enabling condition has been attained at thepoint in time defined by the jackknife determining information. If it isdetermined that a jackknife enabling condition is present at theparticular point in time, a routine may also determine an applicablecountermeasure or countermeasures to implement. Accordingly, in someembodiments, an applicable countermeasure will be selected dependentupon a parameter identified as being a key influencer of the jackknifeenabling condition. However, in other embodiments, an applicablecountermeasure will be selected as being most able to readily alleviatethe jackknife enabling condition. In still another embodiment, apredefined countermeasure or predefined set of countermeasures may bethe applicable countermeasure(s).

As previously disclosed with reference to the illustrated embodiments,during operation of the trailer backup assist system 10, a driver of thevehicle 14 may be limited in the manner in which steering inputs may bemade with the handwheel 68 of the vehicle 14 due to the steered wheels64 of the steering system 62 being directly coupled to the handwheel 68.Accordingly, the steering input device 18 of the trailer backup assistsystem 10 may be used for inputting a desired curvature 26 of thetrailer 12, thereby decoupling such commands from being made at thehandwheel 68 of the vehicle 14. However, additional embodiments of thetrailer backup assist system 10 may have the capability to selectivelydecouple the handwheel 68 from movement of steerable wheels of thevehicle 14, thereby allowing the handwheel 68 to be used for commandingchanges in the desired curvature 26 of a trailer 12 or otherwiseselecting a desired backing path during such trailer backup assist.

Referring now to FIG. 7, one embodiment of the steering input device 18is illustrated disposed on a center console 108 of the vehicle 14proximate a shifter 110. In this embodiment, the steering input device18 includes a rotatable knob 30 for providing the controller 28 with thedesired backing path of the trailer 12. More specifically, the angularposition of the rotatable knob 30 may correlate with a desiredcurvature, such that rotation of the knob to a different angularposition provides a different desired curvature with an incrementalchange based on the amount of rotation and, in some embodiments, anormalized rate, as described in greater detail herein.

The rotatable knob 30, as illustrated in FIGS. 7-8, may be biased (e.g.,by a spring return) to a center or at-rest position P(AR) betweenopposing rotational ranges of motion R(R), R(L). In the illustratedembodiment, a first one of the opposing rotational ranges of motion R(R)is substantially equal to a second one of the opposing rotational rangesof motion R(L), R(R). To provide a tactile indication of an amount ofrotation of the rotatable knob 30, a force that biases the knob towardthe at-rest position P(AR) can increase (e.g., non-linearly) as afunction of the amount of rotation of the rotatable knob 30 with respectto the at-rest position P(AR). Additionally, the rotatable knob 30 canbe configured with position indicating detents such that the driver canpositively feel the at-rest position P(AR) and feel the ends of theopposing rotational ranges of motion R(L), R(R) approaching (e.g., softend stops). The rotatable knob 30 may generate a desired curvature valueas function of an amount of rotation of the rotatable knob 30 withrespect to the at-rest position P(AR) and a direction of movement of therotatable knob 30 with respect to the at-rest position P(AR). It is alsocontemplated that the rate of rotation of the rotatable knob 30 may alsobe used to determine the desired curvature output to the controller 28.The at-rest position P(AR) of the knob corresponds to a signalindicating that the vehicle 14 should be steered such that the trailer12 is backed along a substantially straight backing path (zero trailercurvature request from the driver), as defined by the longitudinaldirection 22 of the trailer 12 when the knob was returned to the at-restposition P(AR). A maximum clockwise and anti-clockwise position of theknob (i.e., limits of the opposing rotational ranges of motion R(R),R(L)) may each correspond to a respective signal indicating a tightestradius of curvature (i.e., most acute trajectory or smallest radius ofcurvature) of a path of travel of the trailer 12 that is possiblewithout the corresponding vehicle steering information causing ajackknife condition.

As shown in FIG. 8, a driver can turn the rotatable knob 30 to provide adesired curvature 26 while the driver of the vehicle 14 backs thetrailer 12. In the illustrated embodiment, the rotatable knob 30 rotatesabout a central axis between a center or middle position 114corresponding to a substantially straight backing path 26 of travel, asdefined by the longitudinal direction 22 of the trailer 12, and variousrotated positions 116, 118, 120, 122 on opposing sides of the middleposition 114, commanding a desired curvature 26 corresponding to aradius of the desired backing path of travel for the trailer 12 at thecommanded rotated position. It is contemplated that the rotatable knob30 may be configured in accordance with embodiments of the disclosedsubject matter and omit a means for being biased to an at-rest positionP(AR) between opposing rotational ranges of motion. Lack of such biasingmay allow a current rotational position of the rotatable knob 30 to bemaintained until the rotational control input device is manually movedto a different position. It is also conceivable that the steering inputdevice 18 may include a non-rotational control device that may beconfigured to selectively provide a desired curvature 26 and to overrideor supplement an existing curvature value. Examples of such anon-rotational control input device include, but are not limited to, aplurality of depressible buttons (e.g., curve left, curve right, andtravel straight), a touch screen on which a driver traces or otherwiseinputs a curvature for path of travel commands, a button that istranslatable along an axis for allowing a driver to input backing pathcommands, or a joystick type input and the like.

Referring to FIG. 9, an example of using the steering input device 18for dictating a curvature of a desired backing path of travel (POT) ofthe trailer 12 while backing up the trailer 12 with the vehicle 14 isshown. In preparation of backing the trailer 12, the driver of thevehicle 14 may drive the vehicle 14 forward along a pull-thru path (PTP)to position the vehicle 14 and trailer 12 at a first backup position B1.In the first backup position B1, the vehicle 14 and trailer 12 arelongitudinally aligned with each other such that a longitudinalcenterline axis L1 of the vehicle 14 is aligned with (e.g., parallelwith or coincidental with) a longitudinal centerline axis L2 of thetrailer 12. It is disclosed herein that such alignment of thelongitudinal axis L1, L2 at the onset of an instance of trailer backupfunctionality is not a requirement for operability of a trailer backupassist system 10, but may be done for calibration.

After activating the trailer backup assist system 10 (e.g., before,after, or during the pull-thru sequence), the driver begins to back thetrailer 12 by reversing the vehicle 14 from the first backup positionB1. So long as the rotatable knob 30 of the trailer backup steeringinput device 18 remains in the at-rest position P(AR) and no othersteering input devices 18 are activated, the trailer backup assistsystem 10 will steer the vehicle 14 as necessary for causing the trailer12 to be backed along a substantially straight path of travel, asdefined by the longitudinal direction 22 of the trailer 12, specificallythe centerline axis L2 of the trailer 12, at the time when backing ofthe trailer 12 began. When the trailer 12 reaches the second backupposition B2, the driver rotates the rotatable knob 30 to command thetrailer 12 to be steered to the right (i.e., a knob position R(R)clockwise rotation). Accordingly, the trailer backup assist system 10will steer the vehicle 14 for causing the trailer 12 to be steered tothe right as a function of an amount of rotation of the rotatable knob30 with respect to the at-rest position P(AR), a rate movement of theknob, and/or a direction of movement of the knob with respect to theat-rest position P(AR). Similarly, the trailer 12 can be commanded tosteer to the left by rotating the rotatable knob 30 to the left. Whenthe trailer 12 reaches backup position B3, the driver allows therotatable knob 30 to return to the at-rest position P(AR) therebycausing the trailer backup assist system 10 to steer the vehicle 14 asnecessary for causing the trailer 12 to be backed along a substantiallystraight path of travel as defined by the longitudinal centerline axisL2 of the trailer 12 at the time when the rotatable knob 30 was returnedto the at-rest position P(AR). Thereafter, the trailer backup assistsystem 10 steers the vehicle 14 as necessary for causing the trailer 12to be backed along this substantially straight path to the fourth backupposition B4. In this regard, arcuate portions of a path of travel POT ofthe trailer 12 are dictated by rotation of the rotatable knob 30 andstraight portions of the path of travel POT are dictated by anorientation of the centerline longitudinal axis L2 of the trailer 12when the knob is in/returned to the at-rest position P(AR).

In the embodiment illustrated in FIG. 9, in order to activate thetrailer backup assist system 10, the driver interacts with the trailerbackup assist system 10 and the automatically steers as the driverreverses the vehicle 14. As discussed above, the driver may command thetrailer backing path by using a steering input device 18 and thecontroller 28 may determine the necessary steering command to achievethe desired curvature 26, whereby the driver controls the throttle andbrake while the trailer backup assist system 10 controls the steeringangle.

With reference to FIG. 10, a method of operating one embodiment of thetrailer backup assist system 10 is illustrated, shown as one embodimentof the operating routine 132 (FIG. 2). At step 134, the method isinitiated by the trailer backup assist system 10 being activated. It iscontemplated that this may be done in a variety of ways, such a making aselection on the display 82 of the vehicle HMI 80. The next step 136determines the kinematic relationship between the attached trailer 12and the vehicle 14. To determine the kinematic relationship, variousparameters of the vehicle 14 and the trailer 12 must be sensed, input bythe driver, or otherwise determined for the trailer backup assist system10 to generate steering commands to the power assist steering system 62in accordance with the desired curvature or backing path 26 of thetrailer 12. As disclosed with reference to FIGS. 3 and 6, the kinematicparameters to define the kinematic relationship include a length of thetrailer 12, a wheel base of the vehicle 14, a distance from a hitchconnection to a rear axle of the vehicle 14, and a hitch angle γ betweenthe vehicle 14 and the trailer 12, among other variables and parametersas previously described. Accordingly, after the kinematic relationshipis determined, the trailer backup assist system 10 may proceed at step160 to determine the current hitch angle with the hitch angle sensor 44.It is also conceivable that in some embodiments the hitch angle may beestimated additionally or alternatively with other devices, such as asensor module having a yaw rate sensor attached to the trailer used inconjunction with a vehicle yaw rate sensor to calculate an estimate ofthe hitch angle. Further, it is contemplated that in additionalembodiments of the trailer backup assist system 10 that the steps ofdetermining the kinematic relationship and sensing the hitch angle γ mayoccur before the trailer backup assist system 10 is activated or at anyother time before steering commands are generated.

Still referring to FIG. 10, at step 162, the position changes arereceived from the steering input device 18, such as the angular positionof a secondary steering input device, such as the rotatable knob 30, fordetermining the desired curvature 26. With the determined desiredcurvature 26, at step 164, a steering command may be generated based onthe desired curvature 26, correlating with the position of the steeringinput device 18. The steering commands generated may be generated inconjunction with the processing of the curvature routine 98 and thesteering angle limitation routine 130, among other conceivable routinesprocessed by the controller 28.

With reference to FIG. 11, one embodiment of the steering anglelimitation routine 130 is illustrated, which may be processed inparallel with the operating routine 132, although it is contemplatedthat the operating routine 132 may be modified in additional embodimentsto incorporate the steps of the steering angle limitation routine 130,as described herein. The depicted embodiment includes the preliminarysteps 168 and 170 of sensing the hitch angle γ and sensing the reversingspeed of the vehicle, respectively. As mentioned above, the hitch angleγ may be previously determined at step 160 of the operating routine 132and the speed of the vehicle 14 may be sensed with the speed sensor 58on the vehicle, among other potential ways of the determining the hitchangle γ and the speed.

Still referring to FIG. 11, after the preliminary steps 168 and 170, theillustrated embodiment includes step 172 of determining the maximumhitch angle rate for the steering system. According to one embodiment,the maximum hitch angle rate may be preset based on a maximumcontrollable steering angle rate of the vehicle. As previouslymentioned, the maximum controllable steering angle rate of the vehiclemay be determined by the capabilities of the steering system 62 of theparticular vehicle 14 and may be a default static value or maydynamically update based on operating conditions or other conceivablefactors. In an additional embodiment, the maximum hitch angle rate mayalso be continuously regenerated and defined as a function of the speedof the vehicle 14. It is also contemplated that the maximum hitch anglerate may be additionally or alternatively determined with incorporatingother variables, such as a length of the trailer 12. In additionalembodiments, step 172 may be performed before the preliminary steps 168and 170 or in conjunction with other routines of the trailer backupassist system 10.

With the continued reference to FIG. 11, at step 174 the controller 28of the trailer backup assist system 10 may generate adaptive steeringangle limits 23, which according to one embodiment may be based upon themaximum hitch angle rate, the hitch angle γ, and the reversing speed ofthe vehicle 14. With the adaptive steering angle limits 23 generated,the trailer backup assist system 10 may control the steering angle δ ofthe vehicle 14 within the adaptive steering angle 23 limits to guide thetrailer on a desired backing path, preventing the steering system 62from exceeding the maximum hitch angle rate, and thereby avoid undesiredhitch angle conditions outside the desired curvature 26, such as ajackknife condition

The adaptive steering angle limits 23 are typically generated within thephysical angle limits 20 of the steering system 62, as the steeringangle δ is inherently prevented from exceeding physical angle limits 20.The adaptive steering angle limits 23 may be continuously regenerated inincrements of time based on the changes to the speed of the vehicle 14and the hitch angle γ. In one embodiment, the adaptive steering anglelimits 23 may be defined with the following equations:

${SWA}_{1} = {\delta_{1}*{GR}*\frac{180}{\prod}}$${SWA}_{2} = {\delta_{2}*{GR}*\frac{180}{\prod}}$${Where},{\delta_{1} = {\tan^{- 1}\left( {\frac{W}{L}\left( {{\frac{D}{v\;\cos\;\gamma}*c} - {\tan\;\gamma}} \right)} \right)}},{and}$$\delta_{2} = {{\tan^{- 1}\left( {\frac{W}{L}\left( {{{- \frac{D}{v\;\cos\;\gamma}}*c} - {\tan\;\gamma}} \right)} \right)}.}$

As shown in FIG. 12, the physical and adaptive steering angle limits 20,23 are depicted for a trailer backup assist system 10 with a maximumhitch angle rate of 10 deg/s and a vehicle 14 with a wheelbase W of3.683, a distance L from the rear axle to the hitch of 1.386, and atrailer 12 with a length D of 3.225. As shown, the adaptive steeringangle limits 23 are shown for a speed of 2 kph and 7 kph.

Referring again to FIG. 11, at step 176 the controller 28 may proceed togenerate a steering command based on the desired curvature 26, thesensed hitch angle γ, and the kinematic relationship. The desiredsteering angle of the steering command is then evaluated at step 178 todetermine if it is within the physical and adaptive angle limits 20, 23.If the initially generated steering angle is outside either of thephysical or adaptive angle limits 20, 23, at step 180 the mostrestrictive of the physical and adaptive angle limits 20, 23 that areclosest to the desired steering angle will be set as the steeringcommand. The combination of steps 178 and 180 generate a steeringcommand within the physical and adaptive angle limits 20, 23 that guidesthe trailer 12 toward the desired curvature 26 and prevents the hitchangle γ from approaching a jackknife condition. More specifically, theadaptive angle limits 23 prevent the jackknife condition by onlyallowing the trailer 12 to be on the desired curvature 26 when the hitchangle rate is below the maximum rate determined or otherwise selected.This allows the steering angle δ to adjust with changes to the hitchangle γ, such that the rate of change of the hitch angle γ, i.e. thehitch angle rate, slows and eventually reaches zero as the vehicle 14and the trailer 12 reach the steady state condition for the desiredcurvature 26, not overshooting the desired curvature 26. Further,generating the steering command within the physical and adaptive anglelimits 20, 23 allows the vehicle to operate at higher speeds, whilestill maintaining the same hitch angle rate limits as those achieved atlower speeds. With the generated steering command, the steering anglelimitation routine 130 directs at step 182 for the controller 28 toproceed with the operating routine 132.

As shown in the embodiment depicted in FIG. 10, at step 166, thesteering commands are executed to guide the trailer 12 on the desiredcurvature 26 provided by the steering input device 18. In addition toadjusting the steering angle δ, it is contemplated that additionalembodiments of the operating routine 132 may employ the braking system72 of the vehicle 14 to autonomously limit the speed of the vehicle 14to aid in reducing the hitch angle rate. It is also contemplated thatadditional embodiments may limit the speed and acceleration of thevehicle 14 and trailer 12 with other systems, such as the vehiclepowertrain system 74 and/or a trailer braking system, if available.

Referring again to FIG. 12, the operational possibilities of anexemplary embodiment of the steering angle limitation routine 130 isdepicted with the steering angle δ shown as the corresponding steeringwheel angle. As shown, the physical steering angle limits 20 areconstant for the steering system 62 of the vehicle 14 at a staticsteering angle defined by the operational constraints of the steeringsystem. In contrast to the physical steering angle limits 20, theadaptive steering angle limits 23 are shown as substantially linearfunctions having a negative slope for the adaptive steering angle limits23 across the potential hitch angles at two different vehicle speeds, 2kph and 7 kph. As such, the adaptive steering angle limits 23 can beenseen to decrease and further limit the potential steering angle as thehitch angle γ increases in both positive and negative directions awayfrom the zero hitch angle. These adaptive steering angle limits 23prevent the steering wheel angle from creating a hitch angle rate thatcannot be recovered by the steering system. In some embodiments, thesteering system is controllable below a threshold rate, such as acontrollable steering angle rate between 300 to 600 degrees per second,that is configured to control a corresponding hitch angle rate, whichmay also be dependent upon the specific geometry of the trailer 12 andthereby the kinematic relationship with the vehicle 14. However, theadaptive steering angle limits 23 are greater than the physical steeringangle limits 20 in the steering direction toward the zero hitch angle asthe hitch angle γ increases beyond approximately 15 degrees in theillustrated embodiment. It is contemplated that in additionalembodiments the physical and adaptive steering angle limits 20, 23 maybe non-linear functions and alternatively configured from thoseillustrated herein.

With reference to FIG. 13, a more detailed embodiment of the steeringsystem 62 is shown identifying a steering angle controller 200 thatreceives signals from multiple autonomous steering modules, namely thetrailer backup assist system 10 as well as a park assist system 202. Thesteering angle controller 200 of the illustrated embodiment of thesteering system 62 receives signals from several vehicle sensors,including a steering wheel angle sensor 67, a steering torque sensor 70,and a vehicle speed sensor 58. In one embodiment, these sensor signalsare transmitted over a vehicle communication network, such as a CAN bus,and received by the steering angle controller 200 in combination withcommands from the trailer backup assist system 10 and/or the park assistsystem 202. These sensor signals and steering commands are processed bya microprocessor 204 of the steering angle controller 200 to operate thesteering angle of the steered wheels 64 via the electric steering motor66. The park assist system 202, according to one embodiment, includes aroutine to autonomously steer a vehicle into a selected parking spot,such as in a parallel parking situation. It is contemplated that thepark assist system 202 may include the potential to perform one or moretypes of parking maneuvers, such as parallel parking and perpendicularparking.

Without appropriate arbitration control logic, simultaneous oroverlapping steering commands from different steering modules, such asthe trailer backup assist system 10 and the park assist system 202, maybe commanded to the electric steering motor 66, which could result in asteering angle command or the resulting torque exceeding a predefinedlimiting value and result in undesirable steering behavior and potentialdamage to the steering system 62 or other vehicle components or systems.Accordingly, as shown in FIG. 13, the steering angle controller 200includes an angle-based steering control routine 206 and a torque signalcompensation routine 210 stored in memory 208 of the steering anglecontroller 200 for processing by the microprocessor 204. It iscontemplated that the steering angle controller 200 in the alternativeor in addition to the microprocessor 204 may include other analog and/ordigital circuitry for processing one or more routines. Also, it shouldbe appreciated that the steering angle controller 200 may be astand-alone dedicated controller or may be a shared controllerintegrated with other control functions, such as integrated with thecontroller 28 of the trailer backup assist system 10, and otherconceivable onboard or off-board vehicle control systems.

Referring now to FIGS. 14-16, the angle-based steering control routine206 is configured to receive one or more steering angle commands frommultiple steering modules and to generate a refined steering anglecommand for the steering angle controller 200 to operate the steeredwheels 64 of the vehicle. To arbitrate and control the steering system62, the angle-based steering control routine 206 of the steering anglecontroller 200 is configured to receive the steering angle commands frommultiple steering modules and generate a refined steering angle commandfor the steering angle controller 200 to operate the steered wheels 64of the vehicle 14. The steering angle controller 200 receives themultiple steering angle commands and generates the refined steeringangle command for steering the vehicle 14 based on acceptable steeringcolumn torque conditions for the respective steering module. As such,the refined steering angle command may be substantially equal to one ofthe steering angle commands when the other potential steering anglecommands have transitioned to an inactive arbitration state.

As shown in FIG. 14, one embodiment of an arbitration flow chart 216 isdepicted, which may be contained in the control logic for eachrespective autonomous steering module, including the park assiststeering module 202 and the trailer backup assist steering module 10.Each steering module may be initiated in the closed condition 218, whichprevents the steering module from generating any steering angle commandsover the vehicle communication network to the steering angle controller200. For the respective autonomous steering module to move from theclosed condition 218 to the open condition 220, several parameter staterequirements must be present, such that the vehicle engine and thesteering system 62 are running in acceptable states to receive andexecute a command from the respective autonomous steering module. Forinstance, the vehicle speed must be below a threshold speed, thesteering column torque must be below a threshold torque, and thesteering column speed must be below a threshold speed. Once in the opencondition 220, any change to the vehicle systems, including the vehicleengine and the steering system 62, that would result in an unacceptablestate to execute a command will cause the arbitration state to revert tothe closed condition 218, preventing any steering angle commands frombeing generated by the respective steering module.

With further reference to FIG. 14, from the open condition 220, therespective steering module may move to the active condition 222 when, inaddition to the necessary parameter conditions being acceptable for theopen condition 220, the steering wheel angle is acceptable and atransition factor 226 of the output of the respective steering module isgenerally equal to zero. In the active condition 222, the respectivesteering module starts to generate a steering angle command across thevehicle communication network to the steering angle controller 200.

As shown in FIG. 15, one embodiment of a steering module is depictedtransitioning between the open and the active conditions 220, 222, whichincludes a transition factor 226 being applied to the output. Morespecifically, the transition factor is applied during a period ofT_AC_in for the transition to the active condition 222 and a period ofT_AC_out for the transition to the open or fault conditions 220, 224from the active condition 222. The transition factor 226 allows aproportion of the output steering angle command to be transmitted acrossthe vehicle communication network to the steering angle controller 200,so as to avoid abrupt changes in steering angle commands that couldcause undesired operation of the vehicle 14. In the case oftransitioning to the active condition 222, the transition factor 226increases linearly during the period of T_AC_in, which thereby providesa gradual implementation of the output steering angle command until afull output steering angle command is communicated to the steering anglecontroller 200. The transition of one of the steering modules from theopen condition 220 to the active condition 222 will cause the remainingsteering modules to move to the closed condition 218 or anotherconceivable an inactive state, which prevents substantial overlap in theoutput signals from the steering modules. Similarly, in the case oftransitioning out of the active condition 222, the transition factor 226decreases linearly during the period of T_AC_out after moving out of theactive condition 222, which thereby provides a gradual reduction of theoutput steering angle command until no output steering angle command iscommunicated by the respective steering module. Once the active steeringmodule moves back to the open condition 220, the remaining steeringmodules may resume the open condition from the inactive state. It isalso contemplated that the transition factor may be adjustednon-linearly over the periods identified as T_AC_in and T_AC_out, and itis also conceivable that these periods may be lengthened or shortened toaccommodate the desired performance. Also, during operation of asteering module in the active condition 222, a parameter may change andcause the module to move to the fault condition 224, which requires theparameter to be resolved in the closed condition 218 before moving backto the open condition 220. It is contemplated that this transition maybe substantially the same as the transition from the active condition222 to the open condition 220.

The corresponding method for steering angle control, as shown in FIG.16, includes the general steps 228 and 230 of receiving a first steeringangle command from a first steering module and receiving a secondsteering angle command from a second steering module. In one embodiment,the first and second steering modules may be the trailer backup assistsystem 10 and the park assist system 202. As explained above, thearbitration logic 216 controls the steering modules to generate steeringangle commands when an open state condition 220 of the respectivesteering module is present. However, it is conceivable that thetransition factors may allow one steering module to be still beoutputting some steering angle command during the T_AC_out, whileanother steering module starts to transition into the active condition222. Ultimately, at step 236 a refined steering angle command may begenerated with the received steering angle commands for controlling thesteered wheels 64 of the vehicle 14 at step 238, including the pinionangle, based on acceptable steering column torque conditions for thefirst second steering modules. To determine the acceptable steeringcolumn torque conditions, at step 232 a steering torque is sensed by thetorque sensor (FIG. 17) and compensate for inertia and off-center massof the handwheel 68. The refined steering angle command may then begenerated when the steering torque is less than a threshold torque, asdetermined at step 234. Further, the threshold torque is configured tobe exceeded when an object is obstructing rotation of the handwheel, asdescribed in more detail herein. The refined steering angle command maybe substantially equal the received steering angle command when theother steering modules have transitioned to an inactive state.

Referring again to FIG. 13, to accurately control the steering anglewith the refined steering angle command, the steering angle controller200 may also process a torque signal compensation routine 210 thatdetermines a filtered handwheel acceleration based on the handwheelangle, determines an offset torque based on the filtered handwheelacceleration and handwheel mass properties, and ultimately generates acompensated torque signal based on the offset torque and the inputtorque signal. The compensated torque signal compensates for inertia andoff-center mass of the handwheel 68, whereby a high torque valueassociated with a sudden change in direction of the pinion angle isreduced in the refined torque signal to prevent the refined torquesignal from errantly exceeding a torque threshold, which is indicativeof an object obstructing rotation of the handwheel 68 and causes therespective autonomous steering module to be placed in an inactivearbitration state.

As shown in FIG. 17, a handwheel 68 is illustrated showing an exemplarymass center offset 240, which can cause spikes in a torque signalgenerated by a torque sensor on the torsion bar of the steering column,especially when there is a sudden change in direction of the pinionangle. The handwheel angle θ is sensed by the steering wheel anglesensor 67, which in the illustrated embodiment includes a pinion anglesensor 212 (FIG. 13) that senses a pinion angle of the handwheel 68 anda windup angle sensor 214 (FIG. 13) that senses a torsion bar windupangle of the steering column. The torque signal compensation routine 210generates the handwheel angle θ by combining the pinion angle and thewindup angle.

Still referring to FIG. 17, after combining the pinion angle and thewindup angle, the handwheel angle is filtered with a high-pass filterand integrated to determine a filtered handwheel acceleration value. Thesteering angle controller may then determine an offset torque based onthe filtered handwheel acceleration. More specifically, the offsettorque may be calculated with the following equation:T _(OFFSET) =d*sin(SWA+θ)

Where,

d is the distance from the rotational point of the handwheel to itscenter of gravity,

θ is the angle about the rotation point between vertical and the centerof gravity, and

SWA is the filtered handwheel acceleration.

As shown in FIG. 18, the offset torque calculates instantaneousrotational inertia of the handwheel 68 for applying it to the inputtorque signal to define a refined torque signal that compensates forinertia and off-center mass of the handwheel 68. The refined torquesignal is passed through a low-pass filter prior to exiting the torquesignal compensation routine and operating the pinion angle with therefined torque signal. The high torque value associated with a suddenchange in direction of the pinion angle is reduced in the refined torquesignal to prevent the refined torque signal from errantly exceeding atorque threshold. The steering angle controller 200 may also beconfigured to stop autonomous control of the pinion angle when therefined torque signal exceeds a threshold torque. The threshold torquevalue may be set to be exceeded when an object is obstructing rotationof the handwheel 68, such as a driver grasping the handwheel with theintent to take direct, manual control of the steering system 62.

The corresponding method of operating the torque signal compensationroutine 210 is illustrated in FIG. 19. At step 242 in the method, thehandwheel angle is the angle sensed by combining a sensed pinion angleand a sensed torsion bar windup angle. At step 244, a steering commandis generated, such as by the angle-based steering control routine 206,which includes generating an input torque signal. As described above,the torque signal compensation routine 210 integrates the handwheelangle to determine a handwheel acceleration, at step 246, and thenpasses the handwheel acceleration through a high-pass filter todetermine a filtered handwheel acceleration, at step 248. And in turn,an offset torque is determined based on the filtered handwheelacceleration and handwheel mass properties at step 250. A filteredcompensated torque signal is then generated with the offset torque beingapplied to the input torque signal step 252 and then filtered with alow-pass filter at step 254, which compensates for inertia andoff-center mass of the handwheel 68. The autonomous control of thehandwheel angle is then performed, such as by the trailer backup assistsystem 10, based on the filtered compensated torque signal. As shown inFIG. 20A, the filtered compensated torque signal is shown in comparisonwith the measured torque having the offset torque removed, which are thesignals at steps 254 and 252 (FIG. 19), respectively. Further, as shownin FIG. 20B, the filtered compensated torque signal is shown comparisonwith the input torque and the offset torque, which illustrates how thecompensated torque signal compensates for inertia and off-center mass ofthe handwheel 68 prevents the torque signal from errantly exceeding atorque threshold, which is indicative of an object obstructing rotationof the handwheel 68 and causes the respective autonomous steering moduleto be placed in an inactive arbitration state, such as the faultcondition 224.

It will be understood by one having ordinary skill in the art thatconstruction of the described invention and other components is notlimited to any specific material. Other exemplary embodiments of theinvention disclosed herein may be formed from a wide variety ofmaterials, unless described otherwise herein.

For purposes of this disclosure, the term “coupled” (in all of itsforms, couple, coupling, coupled, etc.) generally means the joining oftwo components (electrical or mechanical) directly or indirectly to oneanother. Such joining may be stationary in nature or movable in nature.Such joining may be achieved with the two components (electrical ormechanical) and any additional intermediate members being integrallyformed as a single unitary body with one another or with the twocomponents. Such joining may be permanent in nature or may be removableor releasable in nature unless otherwise stated.

It is also important to note that the construction and arrangement ofthe elements of the invention as shown in the exemplary embodiments isillustrative only. Although only a few embodiments of the presentinnovations have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited. For example,elements shown as integrally formed may be constructed of multiple partsor elements shown as multiple parts may be integrally formed, theoperation of the interfaces may be reversed or otherwise varied, thelength or width of the structures and/or members or connector or otherelements of the system may be varied, the nature or number of adjustmentpositions provided between the elements may be varied. It should benoted that the elements and/or assemblies of the system may beconstructed from any of a wide variety of materials that providesufficient strength or durability, in any of a wide variety of colors,textures, and combinations. Accordingly, all such modifications areintended to be included within the scope of the present innovations.Other substitutions, modifications, changes, and omissions may be madein the design, operating conditions, and arrangement of the desired andother exemplary embodiments without departing from the spirit of thepresent innovations.

It will be understood that any described processes or steps withindescribed processes may be combined with other disclosed processes orsteps to form structures within the scope of the present invention. Theexemplary structures and processes disclosed herein are for illustrativepurposes and are not to be construed as limiting.

It is also to be understood that variations and modifications can bemade on the aforementioned structures and methods without departing fromthe concepts of the present invention, and further it is to beunderstood that such concepts are intended to be covered by thefollowing claims unless these claims by their language expressly stateotherwise.

What is claimed is:
 1. A vehicle steering system, comprising: a firstsensor sensing a pinion angle of a handwheel; a second sensor sensing atorsion bar windup angle; an autonomous steering module generating asteering command having an input torque signal; and a steering anglecontroller configured to determine a filtered handwheel accelerationbased on the pinion angle and the torsion bar windup angle, determine anoffset torque based on the filtered handwheel acceleration, and applythe offset torque to the input torque signal to define a refined torquesignal that compensates for inertia and off center mass of thehandwheel.
 2. The vehicle steering system of claim 1, wherein a hightorque value associated with a sudden change in direction of the pinionangle is reduced in the refined torque signal to prevent the refinedtorque signal from errantly exceeding a torque threshold, and whereinthe torque threshold is configured to be exceeded when an object isobstructing rotation of the handwheel.
 3. The vehicle steering system ofclaim 1, wherein the steering angle controller autonomously operates thepinion angle based on the refined torque signal.
 4. The vehicle steeringsystem of claim 3, wherein the steering angle controller stopsautonomous control of the pinion angle when the refined torque signalexceeds a threshold torque.
 5. The vehicle steering system of claim 1,wherein the refined torque signal is passed through a low-pass filterprior to operating the pinion angle with the refined torque signal. 6.The vehicle steering system of claim 1, wherein the filtered handwheelacceleration is filtered with a high-pass filter after combining thepinion angle and the windup angle.
 7. A vehicle steering system,comprising: a sensor sensing a handwheel angle based on a sensed pinionangle and a sensed torsion bar windup angle; an autonomous steeringmodule generating an input torque signal; and a steering anglecontroller determining a handwheel acceleration based on the handwheelangle, determining an offset torque based on the handwheel acceleration,and generating a compensated torque signal based on the offset torqueand the input torque signal.
 8. The vehicle steering system of claim 7,wherein the sensor includes a first sensor sensing the pinion angle anda second sensor sensing the torsion bar windup angle.
 9. The vehiclesteering system of claim 7, wherein the autonomous steering moduleincludes a trailer backup assist controller for generating a steeringcommand for guiding a trailer in reverse, the steering command havingthe input torque signal.
 10. The vehicle steering system of claim 7,wherein the compensated torque signal is configured to compensate forinertia and off-center mass of a handwheel.
 11. The vehicle steeringsystem of claim 8, wherein a high torque value associated with a suddenchange in direction of the pinion angle is reduced in the compensatedtorque signal to prevent the compensated torque signal from errantlyexceeding a torque threshold.
 12. The vehicle steering system of claim8, wherein the steering angle controller autonomously operates thepinion angle based on the compensated torque signal and stops autonomouscontrol of the pinion angle when the compensated torque signal exceeds atorque threshold.
 13. The vehicle steering system of claim 7, whereinthe compensated torque signal is passed through a low-pass filter priorto operating the handwheel angle with the compensated torque signal, andwherein the handwheel acceleration is filtered with a high-pass filter.14. A method, comprising: sensing an angle of a handwheel based on asensed pinion angle and a sensed torsion bar windup angle; generating asteering command having an input torque signal; determining a handwheelacceleration based on the angle; determining an offset torque based onthe handwheel acceleration; and generating a compensated torque signalbased on the offset torque and the input torque signal to compensate forinertia and off-center mass of the handwheel.
 15. The method of claim14, wherein sensing the angle of the handwheel includes sensing thepinion angle and sensing the torsion bar windup angle, and wherein theangle of the handwheel is based on the pinion angle combined with thetorsion bar windup angle.
 16. The method of claim 14, furthercomprising: generating the steering command for a vehicle guiding atrailer in reverse; and autonomously operating the angle of thehandwheel based on the compensated torque signal.
 17. The method ofclaim 14, wherein the compensated torque signal is passed through alow-pass, and wherein the handwheel acceleration is filtered with ahigh-pass filter.
 18. The method of claim 14, wherein a high torquevalue associated with a sudden change in direction of a pinion angle isreduced in the compensated torque signal to prevent the compensatetorque signal from errantly exceeding a torque threshold.
 19. The methodof claim 14, further comprising: autonomously operating a handwheelangle based on the compensated torque signal and ceasing autonomousoperation of the handwheel angle when the compensated torque signalexceeds a threshold torque.
 20. The method of claim 19, wherein thethreshold torque value is configured to be exceeded when an object isobstructing a predicted change to the handwheel angle.